docs: def sign(message: bytes, sign_key: SignKey) -> Signature:
          """
          Signs the message and returns signature.
  
          :param: message - Message to sign
          :param: sign_key - Sign key
          :return: Signature
          """
  
          logger = logging.getLogger(__name__)
          logger.debug("Bls::sign: >>> message: %r, sign_key: %r", message, sign_key)
  
          c_instance = c_void_p()
          do_call('indy_crypto_bls_sign',
                  message, len(message),
                  sign_key.c_instance,
                  byref(c_instance))
  
          res = Signature(c_instance)
  
          logger.debug("Bls::sign: <<< res: %r", res)
          return res